189
FXUS66 KPQR 271752
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
952 AM PST Thu Nov 27 2025

Updated aviation discussion.

&&

.SYNOPSIS...Wet conditions continue through Thanksgiving as
another frontal system impacts the region, bringing additional
widespread rain and breezy winds. Conditions gradually trend
drier Friday into Saturday with showers largely pinned to higher
terrain features. Snow levels drop to the passes by Saturday
but limited accumulation is anticipated. A cooling trend impacts
the region Sunday into early next week with additional chances
for precipitation arriving on Tuesday.

&&

.DISCUSSION...Thursday morning through Wednesday...The forecast
remains on track from the previous forecast package with very
little change. Satellite imagery early Thursday morning depicts
a compact low pressure system located around 400 miles west of
the WA/OR border with a cold front approaching the WA and OR
coast. Radar imagery shows the band of rain associated with the
cold front moving inland along the coast. The cold front will
move inland through the morning hours, reaching the Cascades by
midday, as the closed low approaches the coast.  Ensemble
guidance is in very good agreement that the low will approach
the coast right around or just north of the WA/OR border late
this afternoon, then slowly weakening and dissipating over the
coastline tonight. Widespread rain will push east of the
Cascades by midday with conditions turning showery for the
afternoon and evening, continuing into Friday morning as the
upper trough associated with the frontal system exits the region.
Rain amounts with this system through Friday morning will be
similar to previous weather systems. Expect 0.15-0.45 inch for
the central and southern Willamette Valley, 0.4-0.75 for the
northern Willamette Valley into the SW Washington lowlands,
0.5-1.5 inches along the coast and Coast Range as well as the
Oregon Cascades south of Clackamas County, and 0.8-2 inches for
the north Oregon and SW Washington Cascades. Snow levels will
remain just above pass level with this second system, as well.

Winds are expected to be the main impact with this system. As
the front moves inland, winds will begin increasing along the
coast this morning and inland this afternoon. Strongest winds
will be late this afternoon through this evening as the low
center reaches the coast and pressure gradients tighten east of
the low center. Some discrepancies remain between the various
sets of guidance as to just how breezy winds will get. The NBM
remains lower than high resolution ensembles like the HREF and
REFS. Given that winds aloft are expected to be elevated (~40-50
knots at 850 mb) with neutral to slightly unstable conditions
present in the boundary layer to facilitate vertical mixing
Thursday afternoon, nudged wind/wind gust values towards the
high resolution ensemble means. With this in mind, expect peak
gusts of 35-45 mph along the coast and Cascades crests, and up
to 25-35 mph for inland valleys (highest Salem to Portland).
However, it`s worth highlighting there is a 10-25% chance for
isolated peak gusts to exceed 45 mph in the north Willamette
Valley into the Portland/Vancouver late afternoon and evening
which would cause additional impacts. We`ll continue to watch
the progression of this low pressure closely. There is high
confidence that winds decrease late tonight into Friday.

Ensemble guidance remains in good agreement that a strong upper
ridge will build in the eastern Pacific Friday afternoon through
the weekend, though a shortwave will move along the flow on
Saturday, producing a slight chance of showers, mainly over the
terrain. Then cold air is likely to funnel into the PacNW behind
this shortwave.

However, uncertainty in the exact location of the shortwave
continues amongst the ensembles, whether it will move over
western WA and OR or more to the east in eastern WA, OR, and
into Idaho. This will affect exactly how much cooler air will
funnel into NW Oregon and SW Washington. If the wave is more to
the west, more colder air will move into NW Oregon and SW
Washington. If the wave is more to the east, the coldest air
will remain east of the Cascades. Latest NBM guidance indicates
less cooling on Sunday morning then previous forecasts with
mainly a 20-40% chance of low temperatures falling below 32
degrees except for up to 50% chance in the Willamette
Valley between Corvallis and Eugene. Monday morning still looks
to have the coolest temperatures with a 40-80% chance of low
temperatures falling below 32 degrees, with highest
probabilities in typical colder spots outside of urban areas,
especially in the Willamette Valley between Corvallis and
Eugene. One thing to note is probabilities of sub- freezing
temperatures around the Portland metro area are only around
5-15% for each day. Probability of temperatures falling to 25
degrees (Cold Weather Advisory criteria) have also decreased
with most lowland locations below 5%, and the cold pocked in
the central/south Willamette Valley mentioned earlier around a
10-25% chance.

By Tuesday, ensembles remain in agreement that a slightly
stronger shortwave and associated frontal system will slide
south from western Canada into the PacNW, breaking down the high
pressure over the region and returning precipitation chances
over the area through Wednesday. Quite a bit of uncertainty
exists in the strength of this system and the impacts associated
with it, though cold weather could stick around in the wake of
it. -99/03

&&

.AVIATION...Shallow, light rain showers continue behind the
departing frontal boundary. Largely MVFR cigs with unrestricted
vis are favored through the mid-afternoon. Intermittent rain
showers may briefly yield MVFR/high-end IFR vis if showers move
over area terminals, however precise timing of these potential
impacts is low confidence. Otherwise, increasing southerly winds
are expected across the region as an area of low pressure nears
the coast, reaching around 20 kt with gusts to 30-35 kt along the
coast and 15 kt with gusts to 25-30 kt inland into this evening.
One exception to this will be west of the Columbia River Gorge,
where offshore flow will continue until the low moves onshore,
yielding continued gusty east winds at KTTD through 00z Fri. These
easterly or southeasterly gusts will also reach to KPDX, however
the flow will ultimately turn out of the south by midday.

As steadier rain arrives by 21-24z Thu, a period of marginal VFR
cigs may be expected inland, however there will remain a 40-50%
chance cigs remain below 3 kft. Vis restrictions to MVFR levels
within light rain are most likely along the coast, 40-60% chances,
and less so inland, 20-40% chances, through the evening and into
tonight as cigs trend back down to MVFR levels at 1-2 kft.
Widespread IFR cigs late in the period remain relatively unlikely,
less than 20% chances across the region. Behind this additional
frontal boundary, wind gusts will weaken below 20 kt as winds turn
out of the southwest to west after 06-12z Fri.

KPDX AND APPROACHES...Largely MVFR conditions expected to continue
into this afternoon, however brief periods of IFR vis within
intermittent rain showers remains possible. After 22-24z Thu,
steadier rainfall may aid in lifting cigs above 3 kft, but there
is a 40% chance conditions instead remain MVFR. Chances for
further MVFR cigs increase late in the period, after 06-09z Fri.
Initial easterly/southeasterly winds will turn out of the south by
20-22z Thu, and increase to around 15 kt with gusts of 25-30 kt.
These gusts are expected to continue through at least 06z Fri
before easing behind the frontal boundary. -36

&&

.MARINE...A closed low pressure system currently located about
450 miles west of the mouth of the Columbia River will move
toward the south Washington coast through Thursday evening,
causing winds to increase during the day. An initial cold front
is expected to move across the coastal waters Thursday morning,
with isolated wind gusts up to 35 kt. More widespread gales are
now expected behind the front as the closed low pressure system
moves through the waters. South to southwesterly winds will
continue increasing through Thursday afternoon, with wind gusts
up to 40 kt likely. Seas will also increase through the day,
becoming steep and hazardous Thursday afternoon through evening,
peaking around 15 to 18 ft at 11-13 seconds. There remains
around a 10% chance that significant wave heights reach 20 ft.
Gale warnings are in place for all waters later Thu morning into
Thu afternoon, and transition into hazardous seas to cover the
large fresh swell that will move into the waters later Thursday.
Conditions ease late Thursday night into Friday as the low
weakens, with seas expected to fall below 10 ft by Friday
afternoon. Hazardous conditions are not expected through the
weekend as weak high pressure builds over the waters. -DH/03

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.

WA...None.

PZ...Small Craft Advisory until 11 AM PST this morning for PZZ210-
     251>253.

     Gale Warning until 6 PM PST this evening for PZZ210-251>253.

     Hazardous Seas Warning from 6 PM this evening to 2 AM PST
     Friday for PZZ210-251>253-271>273.

     Gale Warning until 6 PM PST this evening for PZZ271>273.

&&

$$

www.weather.gov/portland

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